Field of the Invention
The present invention relates to a heat ray-shielding material which has wide reflection wavelength selectivity and a wide reflection frequency band and is excellent in visible light transmission and radio wave transmission.
Description of the Related Art
In recent years, as one of energy saving measures to reduce carbon dioxide emissions, there have been developed heat-ray shielding materials for windows for buildings and automobiles. From the viewpoint of heat ray-shielding properties (solar radiation heat-acquisition rate), materials of heat ray reflective type which produces no reradiation of heat are more desired than heat absorbing materials which reradiates absorbed light into rooms (in an amount of about ⅓ of the solar radiation energy absorbed), and various techniques have been proposed.
For example, Ag metal thin films are generally used as heat ray-reflecting materials for their high reflectance, however, reflect not only visible light and heat rays but also radio waves, and thus such films have problems with their low visible light transmission and low radio wave transmission. To increase the visible light transmission, Low-E-glass (e.g., produced by Asahi Glass Co., Ltd.) utilizing an Ag—ZnO-multilayered film are widely adopted in buildings. However, Low-E glass has a problem with its low radio wave transmission, because an Ag metal thin film is formed on a surface of the glass.
To solve the above problems, for example, there has been an island-shaped Ag particle-attached glass to which radio wave transmission is imparted. There has been proposed a glass, in which granular Ag is formed, by annealing an Ag thin film formed by vapor deposition (see Japanese Patent (JP-B) No. 3454422). However, in this proposal, since granular-shaped Ag is formed by annealing, there are problems in that it is difficult to control the size and the shape of particles, and the area ratio, to control the reflection wavelength and reflection frequency band of heat ray and to increase the visible light transmissivity.
Further, there have been proposed filters using Ag flat-shaped particles as an infrared ray-shielding filters (see Japanese Patent Application Laid-Open (JP-A) Nos. 2007-108536, 2007-178915, 2007-138249, 2007-138250, and 2007-154292). However, these proposals are each intended to be used in plasma display panels, and use particles of small volume in order to improve the absorptivity of light in the infrared wavelength range, and the Ag flat-shaped particles are not used as a material to shield heat rays (material reflecting heat rays).